This invention relates to endless conveyor belt systems wherein the belts are driven in a helical path. These systems convey products of various kinds through a confined space for a certain amount of time for treating the products, as by heating, drying, cooling or freezing them. Since these systems satisfy rigorous hygiene requirements, they are well suited for handling food products.
The conveyor belt as it travels along the superimposed, helically extending belt tiers can be self-supporting on one or both of its edges. By having the spiral conveyor belt being self-supporting, framework across the belt for supporting the belt is not needed. This framework occupies valuable product carrying space. Eliminating the framework reduces the height between the tiers and the overall height of the spiral. An example of a conveying system wherein the belt is self-supporting on both edges is that shown in U.S. Pat. No. 3,938,651, whose entire contents are hereby incorporated by reference. A disadvantage of having the belt being self-supported on the outside edge however is that it is not open at the outside to provide good circulation with cooling or freezing air. Thus, another design is shown in European Patent Application Publication No. 0.293.095.A1 of Cawley, whose entire contents are hereby incorporated by reference. In this application, the tiers at the outside of the helix are supported by a fixed helical guide which is open between the tiers and the inside of the helical belt is self-supported by upstanding spacer plates mounted to articulated belt links.
When the belt is self-supporting on one or both sides, structure is needed to support the lowermost tier of the belt at those edges. The angle or pitch of this lower support tier determines the pitch of the rest of the helical conveying path. A known way for supporting the lowermost tier, which is disclosed in the '651 patent, provides a supplemental conveyor which drives the lowermost tier. Another known way for supporting the lowermost tier, which is disclosed in the Cawley application, supports the tier on a stationary support which may include small rollers.
The conveyor belt through the helical portion thereof can be driven by a drive cage centrally located within the helical belt. The cage has a plurality of vertical driving bars which engage the heads of the bars of the belt and when rotated by an electric motor drive the belt along its helical path. Supplemental positive drives are provided at the inlet and outlet of the conveyor belt relative to the helical portion, that is at both ends of the belt return path, and synchronized with the drive of the drive cage for smooth even belt travel. Such a positive drive helical conveyor system is shown for example in U.S. Pat. No. 4,741,430, which is hereby incorporated by reference.